In recent years, to respond to rapidly increasing traffic demands in a mobile communication system, use of a specific frequency band shared by a plurality of operators and/or a plurality of communication systems for radio communication has been discussed (see Non Patent Document 1, for example). The specific frequency band is, for example, a frequency band not requiring a license (unlicensed band).
To avoid interference with another operator and/or another communication system, a base station and a radio terminal configured to perform radio communication by using such a specific frequency band are requested to perform a clear channel determination process referred to as listen-before-talk (LBT).
The LBT is a procedure in which it is determined, based on received signal strength (interference power), whether or not a target channel in a specific frequency band is available, and only if the target channel is determined to be a clear channel, the target channel is used.